The present invention includes methods and apparatus for sizing, cutting and welding a variety of metal workpieces fabricated from specialty alloys, such as titanium, Inconel.TM., or hybrid stainless steels. More particularly, the High-Precision Sizing, Cutting and Welding Tool System for Specialty Aerospace Alloys is a versatile and highly effective machine tool that is capable of forming meticulously accurate flared surfaces, and is also capable of precisely severing and welding these alloy tubes.
The aerospace industry in the United States is rapidly being confronted with obsolete fabrication technology and equipment that cannot keep pace with the technological requirements of today's and tomorrow's aircraft requirements. Each year the machine tool industry encounters new demands of engineers who specify increasingly complex machining processes for the manufacture of metal parts. One of greatest challenges confronting designers in the precision welding industry is finding more precise and dependable techniques to join metal parts that may have exceedingly small dimensional tolerances or that may be fabricated from exotic alloys, such as titanium, Inconel.TM., or hybrid stainless steels. The aircraft and aerospace industries are constantly confronted by difficulties that arise when hollow cylindrical metal conduits are welded together. These tubes reside within the fuselage or wings of an aircraft and are used to convey fluids or to protect environmental control systems within the vehicle.
Although the existence of titanium was first observed in 1790, a feasible process of producing titanium was not discovered until 1938. Titanium sponge was first developed by W. J. Kroll and was produced using the magnesium reduction of titanium tetrachloride. Shortly thereafter, the United States armed services became interested in titanium because of its high melting point. The first commercial titanium became available around 1950, and the production and use of titanium alloys has increased steadily since that time.
Titanium and its alloys have material properties that make it especially desirable for special applications, particularly within the aerospace industry. First, titanium has a high strength-to-weight ratio, which makes it comparable to many steels and stainless steels, while being only about 56 percent as heavy. While titanium alloys are about 40 percent heavier than aluminum, their greater strength allows much less material to be used for many applications. Titanium alloys also possess good corrosion resistance, and high heat performance which makes them even more desirable for aerospace applications.
Despite the desirable properties that titanium alloys possess, the high cost of the material and difficulties with production and fabrication with titanium alloys have limited their widespread use. Titanium alloys tend to be very unforgiving when standard fabrication methods are employed. They are at least as difficult to work with as hybrid stainless steel alloys. Titanium alloys are also easily contaminated at high temperatures, which can seriously impact the quality of a weld joint in a titanium structure. New techniques would be needed to prepare and weld titanium alloy structures that avoid such contamination and minimize the requirement of additional weld metal.
The basic method of mating metal tubes end-to-end is commonly referred to as "butt welding," and is well known to persons ordinarily skilled in the welding art. The tubes are usually placed in a jig or fixture, aligned, and then welded together using a conventional weldhead. If the dimensions of the two tubes are not precisely matched, conventional "spreader" fixtures, such as that shown in FIG. 1, may be used to try to correct any dimensional mismatch and minimize the differences between the dimensions of the two mating components. This spreader fixture known as a "pie-die", labeled "A" in FIG. 1, includes four sections B, C, D, and E which operate simultaneously and are arranged in a circular pattern about a central point F. All of the sections, which resemble the slices of a pie cut into quarters, move radially away from center point F. The entire device A is placed inside a hollow tube which requires shaping, and then one or more sections B, C, D, or E is forced outward against the workpiece. In FIG. 1, the primed reference numerals B', C', D', and E' indicate the displaced positions of each of the shaping sections. This technique, however, is very limited because the workpiece nearly always has a tendency to spring back to its original position after it is stretched by the "pie-die" spreader. Overcoming this elastic memory or "springback" effect is difficult to accomplish using a non-rotating sectioned spreading device. This conventional method is usually imprecise and may lead to faulty welds that can ultimately crack and break apart.
Previous mechanical devices have employed roller mechanisms to work thin gauge tin, copper, or steel sheet metal to quickly deform these common metals for simple fabricated objects, such as cans, drums, or tube sheets. In U.S. Pat. No. 1,732,861, issued on Oct. 22, 1929, Rosenbloom discloses a simple tool that uses rollers to form flanges out of holes in sheet metal plates, such as tank or drum tops. This device was designed to be operated with a simple drill press. In U.S. Pat. No. 1,543,583, issued on Jun. 23, 1925, Mason discloses a tool that uses a roller mechanism to bell tubes in boilers during the manufacturing process. In U.S. Pat. No. 2,388,643, issued on Nov. 6, 1945, Rode et al. used an apparatus employing swaging dies to taper or swage the outer surface of common seamless tubing. In U.S. Pat. No. 3,811,306, issued on May 21, 1974, Yoshimura discloses a method and apparatus for forming and deburring a cylindrical can fabricated from aluminum or tin plate, which employed rollers to the outside surface of the workpiece.
In U.S. Pat. No. 3,498,245, issued on Mar. 3, 1970, Hansson discloses a roller sizing tool for forming can bodies by working the relatively brittle sheet metal beyond its elastic limit. The Hansson reference discloses rollers (53) that protrude from shanks (54) which pass through bores (56) in a body (46) which contains a complex ball bearing retainer (60, 61, 62, 63 and 64) for each roller (53). A reduced threaded end portion (55) extends from each shank (54) past a washer (58), and is fastened on the opposite side of the body (46) with a nut (57). The rollers (53) are "journalled in the disk-like body 46". (See Hansson, Col. 7, Line 35.) In Hansson's arrangement, the rollers (53), shanks (54) and nuts (57) spin together on an inner ball bearing race (61). Because of the action of the internal ball bearing (60), Hansson's rollers (54) may shift their positions relative to an axis that extends perpendicular to the body (46) when they encounter mechanical resistance presented by the workpiece. This slippage is perfectly acceptable for the process of manufacturing ordinary metal cans, but Hansson' s machine is not capable of performing the precise sizing of specialty aerospace alloys which possess high strength-to-weight ratios, good performance at elevated temperatures, and high corrosion resistance.
Hansson's invention was purposely developed for spin flanging of can body edges. (See Hansson, Col. 1, Lines 2-3.) This operation is rough and crude compared to the precise tolerances involved in the processing of specialty alloys in for the aerospace industry. Hansson clearly states that the object of his invention is to increase the transverse ductility of the edges of a high-strength brittle metal can. (See Hansson, Col. 1, Lines 16-17.) Hansson, however, relied on the malleability of his materials which do not experience hardening as they are formed. He was primarily concerned with reducing the stability of his workpiece. The Hansson reference does not provide for easy repair or replacement of the rollers (14).
While past inventors provided mechanisms for the simple, non-critical fabrication of thin gauge common metals, they designed their devices with the intent to utilize the moderate ductility and malleability of the metals they were working with at that time. They never had to consider the difficulties of dealing with the high ductility that is exhibited by many modern high-strength aerospace alloys that are being prepared for precision welding techniques. Aerospace applications often require the precise weldments of titanium tubing of many diameters and gauge sizes, such as 1" diameter tube with a 0.020" wall thickness, or a 6" diameter with a wall thickness of 0.030" to 0.040".
The problem of providing a high-precision sizing, cutting, and welding tool for use with specialty alloys, such as titanium, Inconel.TM., or hybrid stainless steels, has presented a major challenge to engineers and technicians in the metalworking field. The development of an accurate and versatile system that overcomes the difficulties encountered when conventional welding and metal shaping techniques are employed to fabricate welded titanium, Inconel.TM., or hybrid stainless steel alloy parts would constitute a major technological advance in the metal fabrication business. The enhanced performance that could be achieved using such an innovative device would satisfy a long felt need within the industry and would enable machine tool equipment manufacturers and users to save substantial expenditures of time and money.